This invention relates to an engine idling speed control apparatus arranged to provide a feedback control to correct the amount of air permitted to enter the engine so as to maintain the engine idling speed at a target value when the engine is idling.
For example, Japanese Patent Kokai No. 62-129544 discloses an engine idling speed control apparatus including an auxiliary air control valve provided in an auxiliary air passage bypassing a throttle valve situated within an engine induction passage. The control apparatus is arranged to change the duty factor of an electrical pulse signal applied to operate the auxiliary air control valve in such a manner as to provide a feedback control correcting the air flow through the auxiliary air passage to maintain the engine idling speed at a target value when the engine is idling. The engine idling speed control apparatus is arranged to avoid engine stall by increasing the target engine idling speed value as the external load increases. For this purpose, various switches are required to indicate the conditions of the respective external loads including an air conditioner, a power steering unit, head lights, rear defogers and the like. However, the use of these switches results in an expensive engine idling speed control apparatus. This is true particularly when a number of external loads are used.